This invention relates to an exhaust timing control device for a two-cycle engine and more particularly to an improved arrangement for controlling the flow of exhaust gases from the combustion chamber of an internal combustion engine so as to achieve good performance under all running conditions.
Like many factors in engine design, the timing of exhaust port opening is generally a compromise between good performance at low speeds and good performance at high speeds. Recently, however, it has been determined that the performance of an engine can be increased at the maximum end without sacrificing low speed running if a control valve is utilized in conjunction with the exhaust port so as to delay opening of the exhaust port at low speeds and to cause it to open earlier at high speeds. Such exhaust port controls are frequently employed in conjunction with two-cycle internal combustion engines wherein a main control valve varies the timing of opening of the exhaust port.
In order to further increase the performance of engines, frequently multiple exhaust ports are employed. Where an auxiliary exhaust port is provided, it is also desirable to vary its opening and closing in response to engine running conditions so as to improve performance. In conjunction with two-cycle internal combustion engines and other engines, it is not always possible to put the control for the auxiliary exhaust port directly at the exhaust port. For this reason, prior art type of auxiliary port controls have been on/off type of devices.
In conjunction with the running of prior art engines having both main and auxiliary exhaust ports and controls for each of them with the auxiliary port control being an on/off type of control. It has been found that there is a dip or valley in the torque and power curve that occurs at the time when the auxiliary port control is moved from its closed to its opened position. This can be seen in the curve D in FIG. 1. This is a power to speed curve and it will be seen that at the time when the auxiliary port control opens at approximately 8,000 rpm, there is a dip in the power curve which will coincide with a dip in the torque curve.
It is, therefore, a principal object of this invention to provide an improved exhaust timing control system for engines that will increase the performance at high ends without sacrificing performance under any other running condition.
It is a further object of this invention to provide an improved port control arrangement for engines that will increase maximum performance without any dip in the torque curve or power curve.
It is a further object of this invention to provide an improved port controlling arrangement for two-cycle internal combustion engines.